We are interested in the mechanism of action of volatile anesthetic agents such as halothane (2-bromo-2-chloro-1,1,1-trifluoroethane; molecular weight = 197.4; boiling point = 50.2C; specific gravity = 1.86 at 25 C; vapor pressure = 243 mm Hg at 20 C). While several investigators have shown significant effects of halothane on receptors and other systems of interest, we are taking a more fundamental approach and looking at the interaction between halothane and proteins on a molecular level. We want to understand the nature of the interaction, the energetics, and the stoichiometry. In experiments conducted to date, we have found that halothane increases the stability of bovine serum albumin (2 mg/ml, pH 7, 150 mM NaCl, 10 mM KPO4) in a concentration-dependent manner. The thermal transition midpoint is increased almost 10 C when halothane is dissolved to the maximum extent in aqueous medium (~ 19 mM). Such increased stability may prevent the dynamic structural changes that are normally required for protein function and may ultimately be the mechanism underlying volatile anesthetic action.